Reusable warmers employing a super-cooled aqueous solution and an activator have been used by sportsmen and others for years to warm parts of the human body. Such a reusable warmer is shown, for example, in U.S. Pat. No. 4,077,390 to Stanley et al. (issued Mar. 7, 1978) generally at FIG. 1 and described generally at column 1, line 59 to column 2 line 4 as being a sealed bag-like flexible receptacle (such as polyethylene, nylon and the like) containing a super-cooled aqueous sodium acetate and an activator comprising a flexible metal strip having one or more slits or fissures. Another type of activator is described in my U.S. Pat. No. 4,872,442 (issued Oct. 10, 1989). That activator is characterized by a plurality of slits in a flexible metal article, with the opposing sides of the slits being in contact along at least a part of the length of the slit, and by an eroded and roughened surface on said article which comprises a number of minute metal nodules attached to and protruding from the surface, especially at or near the slit, which nodules are adapted to be detached or broken-off upon flexing of the activator.
The super-cooled sodium acetate solution contained in the bag-like receptacle is activated by flexing or bending the activator strip. Upon activation, the sodium acetate in the super-cooled solution crystallizes and heat (i.e. the "heat of crystallization") is evolved. Reuse of the warmer is accomplished by merely reheating the container contents to dissolve the crystallized sodium acetate and once again form the super-cooled sodium acetate solution. This can be done by either immersing the warmer in boiling water or by heating the warmer in a microwave oven for a time sufficient to dissolve the crystallized sodium acetate.
One of the primary uses for such reusable warmers is the application of heat directly to various parts of the human body to relieve muscle aches and pains. Other uses include those by sports participants (such as hunters, skiers and the like) or sports enthusiasts (such as spectators at sporting events) who use the warmers to keep various parts of their bodies warm during cold weather. However, the human body in general is contoured and not flat. Moreover, the person using the reusable warmer may be standing, sitting or walking. For these reasons the reusable warmer is for the most part not applied in a horizontal position (i.e. not flat).
It has been found that during use the super-cooled aqueous solution in the reusable warmer being a liquid will flow in the plastic bag (as, for example, around a leg or arm) and form areas in the bag having too much solution leaving other areas with too little. This phenomenon has been referred to as "saddle bagging."
Saddle bagging leads to uneven coverage by the reusable warmer of the body part area to be heated. Heretofore, the art has attempted to minimize saddle bagging by various means. These have included, for example, adding welds to the flexible, sealed container of the warmer so that the solution is restrained from freely flowing. Also the use of very heavy gauge plastics which will not only be more resistant to bending, but will also act to restrain flow of the super-cooled solution and keep a more flat surface have been tried. None of these means has proved satisfactory, since they render the reusable warmer less comfortable and more difficult to use. It has been found that users of the reusable warmers prefer relatively flexible containers made of relatively thin materials such as polyethylene and nylon (i.e., low cost, non vinyl packages) and when such materials are used the problem of super-cooled solution migration and the resulting saddle bagging is accentuated and cannot be readily solved by conventional means, as, for example, by weld placement. Adding welds also results in a less flexible and more expensive product.